The present invention relates to a drive with a pair of transverse flux motors coupled between first and second relatively rotatable components.
A transverse flux electrical motor with two rows of elements is described in U.S. Pat. No. 5,289,072. In this design, a rotor is mounted so that it can rotate about a shaft in a stator housing. The rotor comprises a central disk on whose radially outer circumference a pole structure is arranged on each axial side. The pole structure includes a series of permanent magnets arranged in the circumferential direction and polarized in an alternating manner. The pole structures are opposed, separated by an air gap, by a stator consisting of an outer stator located radially on the outside and of an inner stator located radially on the inside. The outer stator includes U-shaped armature elements whose legs stand opposite the permanent magnets of the pole structures. A ring winding running in the circumferential direction of the rotor is inside the legs. The inner stator includes yoke elements forming the magnetic circuits with the permanent magnets.
A transverse flux motor with permanent excitement and a pair of sections or branches is shown in DE-A-35 36 538. In this design individual segments or armature element areas can be disabled or deactivated by their associated inverters. In the case of winding damage, partial segments can be radially removed without disassembling the entire machine, leaving the remaining segments operational.
In comparison to longitudinal flux machines of the same size, transversal flux machines develop a significantly greater torque. They are therefore particularly suitable for direct drives in vehicles and they permit the elimination of expensive and inefficient mechanical transmissions. However, the torque requirements of vehicle drives can vary greatly depending on the type of use. Thus, an especially high torque is demanded from a tractor for use during plowing at a relatively slow travel and low wheel speeds, whereas significantly lower torques are required for a transport operation at relatively high travel speeds and high wheel speeds. Conventional transverse flux machines do not take into account these differing torque requirements. It would be desirable to provide such a transverse flux drive which can be adapted to varying torque requirements.
An object of the present invention is to provide such a transverse flux drive which can be adapted to varying torque requirements.
This and other advantages are achieved by the present invention wherein a transverse flux drive includes first and second relatively rotatable components and a pair of transverse flux motor units coupled therebetween. Each motor unit includes U-shaped armature elements coupled to the first component and permanent magnet pole elements coupled to the second component. The armature elements and the pole elements form circumferentially equidistantly spaced magnetic circuit elements. Each armature element encloses an exciter winding extending in the circumferential direction.
The polarity of the adjacent magnets alternates in the circumferential direction. A soft-iron lamellar packet is preferably arranged between each pair of permanent magnets. According to the invention, one or more of the pole elements can be axially shifted and de-coupled from their magnetic flux circuit.
When shifted, the shifted pole elements are removed from the magnetic field or the magnetic flux so that the total flux of the motor is attenuated. In other words, as a result of an axial shifting of the pole elements, the armature elements are spatially removed from the region of influence of the pole elements so that the affected magnetic circuit is ineffective. The associated pole elements then merely rotate by entrainment and do not contribute to the operative motor force. In the case of only partial axial shifting of the magnetic pole elements, the field attenuation is reduced.
Preferably, the first component, which carries the armature elements and exciter winding, is a non-rotating stator. The second component which carries the magnetic pole elements, is preferably a rotor which is rotatable with respect to the stator. As a result, slip rings for the electrical supply of the exciter winding can be eliminated and no rotary coolant communication are required to cool the exciter winding. The pole elements of each motor unit are preferably arranged in a yoke element which rotates in with a rotor of the transverse flux drive.
Preferably, one motor unit is fixed and the motor unit has elements which can be shifted axially to entirely or partially interrupt the magnetic circuits associated with such elements.
Preferably, the magnetic circuit elements of the two motor units are staggered in relation to each other in a circumferential direction. For example, the armature elements of the two motor units are staggered in the circumferential direction, whereas the magnetic pole elements of the two motor units are not stagger with respect to one another. Alternatively, it is also possible to stagger the magnetic pole elements relative to one another. If only two motor units are used, the offset preferably corresponds approximately to one half the circumferential interval of the particular elements. The result is in a drive in which the flow of the power of the sections is shifted in time so that the machine starts more smoothly and runs more uniformly.
The armature elements of each section are inductively coupled by a single, continuous, exciter winding, such as a concentric ring coil, in order to simplify the design and reduce winding losses.
Preferably, a shifting device makes a shifting possible during the operation of the transverse flux drive. Thus, different torque requirements can be reacted to during the operation without having to stop the drive in order to intervene in the drive system. This is especially advantageous for drive systems of work vehicles because the drive can be adapted to changing torque requirements, such as when changing between the start of the work and the transport operation, without interrupting the operation.
Preferably, a control device detects the drive speed and carries out automatic shifting if a speed limit is exceeded or dropped below. Different speed limits can be set in order to produce shift increase or decrease the flux. It is advantageous for stable operation to shift to lower the flux in the case of a rather low speed limit than to carry out the shifting in the sense of an increase of flux.
The stator housing includes at least one hydraulic chamber which slidably receives a piston which is coupled to at least one pole element. The hydraulic components are thus located in the stator housing so that rotating hydraulic connections are avoided and the hydraulic system is not exposed to the rotary stresses of a rotor.
A return spring engages the piston and is biased to urge the piston into its initial position, in which the pole elements are part of a magnetic flux circuit. In response to hydraulic pressure, the piston can shift entirely or partially into a disengaged position in which the pole element is entirely or partially removed from its magnetic circuit.
Preferably, the transverse flux drive is an integral part of a wheel hub, such as the wheel hub of a work vehicle, so that the rotating component drives a vehicle wheel. The result is a complete yet versatile compact module which unites the drive function and the wheel function. Such a module is especially advantageous in a vehicle with electric individual-wheel drive, such as shown in DE-A-197 23 776 and EP-A-0 864 457. The rotating component preferably forms a rim for a vehicle tire. The rim is cylindrical and has wheel flange on each axial side. One of the wheel flanges can be fastened by a screw connection and can be removed to simplify tire mounting. Preferably, the stator is coupled to a vehicle axle, such as a rigid axle, a steering axle and/or a spring-suspended or non-spring-suspended axle.